I. Field
The present invention relates generally to communication, and more specifically to data transmission in a wireless communication system.
II. Background
Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, multi-media broadcast, text messaging, and so on. These systems may be multiple-access systems capable of supporting communication for multiple users by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, and Orthogonal Frequency Division Multiple Access (OFDMA) systems. A CDMA system may implement a radio access technology (RAT) such as Wideband CDMA (W-CDMA), cdma2000, and so on. RAT refers to the technology used for over-the-air communication. W-CDMA is described in documents from a consortium named “3rd Generation Partnership Project” (3GPP). cdma2000 is described in documents from a consortium named “3rd Generation Partnership Project 2” (3GPP2). 3GPP and 3GPP2 documents are publicly available.
W-CDMA and cdma2000 employ direct sequence CDMA (DS-CDMA) radio technology. DS-CDMA spectrally spreads a narrowband signal over the entire system bandwidth with a spreading code, which is called a scrambling code in W-CDMA and a pseudo-random noise (PN) code in cdma2000. DS-CDMA has certain advantages such as ease of supporting multiple access, narrowband rejection, and so on. However, DS-CDMA is susceptible to frequency selective fading, which is a frequency response that is not flat across the system bandwidth. Frequency selective fading results from time dispersion in a wireless channel and causes intersymbol interference (ISI), which can degrade performance. A complicated receiver with an equalizer may be needed to combat the intersymbol interference.
There is therefore a need in the art for a wireless communication system capable of supporting multiple users and providing improved performance.